The invention relates to a self-emptying clarifying drum having a paring disk disposed in a paring chamber for the removal of the clarified liquid, and an automatically operating apparatus for sensing the level of solids in the separating chamber of the drum, this apparatus consisting of a plurality of passages formed by a separating plate and the drum cover and leading from the separating chamber to a paring chamber provided with a paring disk for the derivation of a small portion of the clarified liquid, the outlet passage of the paring disk being connected on the one hand to the outlet of the clarifying phase and on the other hand to a measuring device which in turn cooperates with a control apparatus for the initiation of the discharge of the solids from the drum.
Self-emptying clarifying drums of this construction are known, for example, from German Offenlegungsschrift No. 2,436,285, and they are used for the purpose of initiating partial or complete discharge operations of the drum whenever a predetermined amount of solids has collected in the separating chamber of the drum. For this purpose, during the clarifying process in the drum a small portion of clarified liquid is continuously fed through one or more passages leading from the separating chamber and formed by segment-shaped chambers separated from one another by ribs between the drum cover and the separating plate and is conveyed to a paring chamber equipped with a paring disk. The liquid removed by this paring disk is fed to a measuring device, e.g., a flow meter, and delivered to the clear phase outlet. The flow meter is connected to a control apparatus which starts a partial or complete emptying of the drum whenever the rate of flow in the flow meter decreases. For this purpose an actuation point is provided on the flow meter. The rate of flow in the flow meter diminishes whenever the solid matter spun out in the separating chamber has collected up to the outer edge of the separating plate and thus blocks the passages disposed above the separating plate.
The outer diameter of the separating plate and thus the inlet to the passages determines the permissible volume of the spun-out solids and thus prevents the solids from accumulating to the point of contact with the plate stack disposed in the drum. The permissible volume of removable solids in the drum is primarily determined by their nature, i.e., their consistency, since otherwise the complete discharge of the solids from the drum would not be assured. The volume of the allowable amount of solids can be no more than small in the case of dense solids, but in the case of bulky solids it can be larger.
The disadvantage of the known self-emptying clarifying drums of the above-named type of construction is that the volume of removable solids is determined by the outer inlet cross section of the passages and hence by the separating plate diameter, and is based on the solids that are the hardest to discharge. In these known clarifying drums, accordingly, only a very specific amount of solids can be discharged, which often is too small without replacing the separating plate, resulting in the necessity of a great number of emptying operations if the content of solids in the liquid is great. Losses of clarified liquid nevertheless often occur in the emptying operations, especially in the total emptying of the drum.